Plastic Waste Sorting via NIR Spectroscopy and Size Fractionation
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Solution Overview
Problem
Current methods for processing mixed plastics waste are inefficient in separating different types of plastics, leading to contamination and low purity of recycled materials, which is exacerbated by the need for processes that can adapt to changing industrial recycling capabilities.
Innovation Solution
A method involving mechanical and near-infrared spectroscopy sorting to separate plastics into three grades (Tier 1, Tier 2, and Tier 3) by size fractionation, metallic object removal, and multiple passes through near-infrared separators to achieve high purity, with additional manual sorting for quality control, and the use of computer program code to control the sorting process.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If mechanical separation and basic sorting methods are used, then processing speed and productivity are maintained, but the purity of plastic streams remains low (around 70%) due to contamination from different plastic types
Solution Approach 1:
The waste material is divided into multiple size fractions through screening, and each fraction is processed separately through the sorting system. This segmentation allows the near-infrared spectroscopy sorter to focus on specific size ranges, improving detection accuracy and stream purity while managing system complexity through modular processing stages
Solution Approach 2:
The patent replaces basic mechanical sorting methods with near-infrared spectroscopy-based sorting. This substitution enables identification and separation of different plastic types based on their molecular structure rather than just physical properties, significantly increasing stream purity from 70% to over 90% while maintaining automated processing
2Manufacturing precision
If multiple sorting passes and manual sorting are implemented, then the purity of plastic streams increases to over 90%, but the processing time and operational complexity increase
Solution Approach 1:
The waste material undergoes preliminary size fractionation through screening before entering the main sorting process. This preliminary action organizes the material into manageable size fractions, enabling more efficient subsequent sorting passes and reducing the time required for achieving high purity levels
Solution Approach 2:
The sorting process is implemented in multiple periodic passes through the near-infrared spectroscopy sorter. Each pass progressively removes contaminants and improves purity, with the system cycling through the same sorting mechanism multiple times rather than using a single complex sorting operation, thereby managing processing time through repeated simplified actions
3Manufacturing precision
If size fractionation and multiple sorting streams are created, then different plastic types are effectively separated into Tier 1, Tier 2, and Tier 3, but the device complexity and number of processing steps increase
Solution Approach 1:
The sorting system divides waste material into multiple size fractions and creates separate processing streams (Tier 1, Tier 2, Tier 3) for different plastic types. Each stream is handled independently through the near-infrared spectroscopy sorter, enabling precise separation of plastic types while maintaining a modular system architecture that manages complexity through standardized processing modules
Solution Approach 2:
The near-infrared spectroscopy sorter serves as a universal sorting device that handles all plastic types across all size fractions and streams. This multi-functional device replaces the need for multiple specialized sorting machines, achieving high separation accuracy while reducing overall system complexity by consolidating sorting capabilities into a single advanced device
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The method increases the purity of plastic streams from approximately 70% to over 90%, meeting the requirements for recycling and reprocessing, such as monomer production via thermal depolymerization, by effectively separating and purifying polypropylene, polyethylene, polyurethane, and other plastics.
Implementation Method 1
mechanically sorting the at least two streams, using near-infrared spectroscopy, to produce at least three product streams
Data Source
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AI summary
A method of processing waste is described for the recovery of various grades of plastics products for onward processing. The method includes receiving waste material; shredding the waste material; mechanically separating the waste material into at least three size fractions; removing at least some metallic objects from one of the at least three size fractions; splitting the one size fraction, after at least some metallic objects have been removed from it, into at least two streams; mechanically sorting the at least two streams, using near-infrared spectroscopy, to produce at least three product streams, a first product stream comprising substantially only one or more of polypropylene plastics, polyethylene plastics and polybromide plastics, a second product stream comprising substantially only one or more of polyethylene terephthalate (PET) plastics, polyethersulfone plastics and polycarbonate plastics, and a third product stream comprising substantially only one or more of polyurethane plastics, PVC plastics, polystyrene plastics, polyamide plastics, ABS, PTFE, latex and silicone plastics.